Study of the Hydration-Dehydration in Polyelectrolyte Solutions by use Ultrasonic Technique

Abstract

In this study, the ultrasonic velocity and the density of the polycarboxylic acid solutions which are neutralized at various degrees by sodium hydroxide or tetra-n-butyl ammonium hydroxide have been measured. From these results, the amount of hydrated water molecules has been estimated. An abnormal behavior of hydration has been found in polyacid solutions neutralized by NaOH, which is interpreted as being due to the partial dehydration resulting from Na ion-polyion binding at high degree of neutralization. The effects of adding various mono- or di-valent salts upon the hydration state of polyanion were also examined. From these experiments, it has been found that Ba ion-polyion binding gives rise to 40 percent dehydration of the water molecules which were hydrated in no binding state, and Mg ion-polyion binding gives rise to 20 percent dehydration. The whole results in polyacids were always compared with the results in monoacids, and it was concluded that the above dehydration phenomenon was one of the important characteristics of polyacids.